Hydraulic fracturing accounted for more than one-half of U.S. oil production and two-thirds of U.S. gas production in 2015, according to U.S. Energy Information Administration. Moreover, that percentage is expected to continue to rise as more states undertake hydraulic fracturing to recover reserves held deep within the Earth. While the practice typically produces less greenhouse gas emissions than older technologies such as coal, notes researchers at Penn State, it produces wastewater — as much as 1.7 billion gallons in 2015. Dealing with this wastewater effectively — to protect a finite resource — is the focus of research on several fronts. The results point to a guardedly optimistic outlook.

To get a better understanding of how the contaminants contained in the wastewater may affect the environment, Penn State environmental engineering professor Bill Burgos and his colleagues are studying sediment samples from a water reservoirs and lakes in areas near the fracking operations. Though the research shows the discharge is affecting water and sediment quality, the long-term effects are unknown for now.

In Houston, researchers at Rice University are exploring reusable, carbon nanotube-reinforced filters to remove toxins from fracking wastewater. Rice chemist Andrew Barron and his colleagues say the ceramic membrane has been shown to remove more than 90 percent of hydrocarbons, bacteria and particulates from fracking operations. The work is reported in Nature’s open-access Scientific Reports. The filters’ effectivity is credited to the ultra-small pores — about one-fifth of a micron wide — in the filter material. Because the pores are ionically charged, a thin layer of water adheres to the filter surface and repels hydrocarbons and oils that would otherwise clog the filter.

Barron is quick to note that no one type of filter can remove every type of contaminant found in fracking wastewaters. “Solubilized hydrocarbon molecules slip right through microfilters designed to remove bacteria. Natural organic matter — like sugars from guar gum used to make fracking fluids more viscous — require ultrafiltration or nanofiltration, but those foul easily, especially from hydrocarbons that emulsify into globules. A multistage filter that could remove all the contaminants is not practical due to cost and the energy it would consume,” according to a report by Rice University.